Electric discharge device



J. w. FULTON I ELECTRIC DIS'GHARGE DEVICE May 14, 1946.

Filed Feb. 10, 1945 {fix/enter: John W. Fulton,

l-hs Attorney Patented May 14, 1946 v York Application-February 10,1945, Serial No. 577,198

' effective, however, the getter material-'in'anew tube should be free of gas. To this end; it has heretofore been sought to outgas the getter during exhaustion of the tube,-by-heating the getter with high frequencytotemperatures outside the range attained under operating conditions.- A tantalum getter, for example, readily absorbs gases in an operating temperature range of. some 800 C. to 1600 0., and the -resultingcompounds are readily broken'down to liberate the'gasin a high temperature range "of some x1800 C, to

1'5 Qlairns. (c1. ate-#275) In sometubes, "however; heating: the *getter material by highirequency 'during the exhaustion is impracticable, so: that it .has heretofore been impossible to makethemost efiectiveuse of the getter insuch tubes. :In-acc'ordance with'an important: aspect. of my invention,. I provide an improved structure, employing a getter-material of this type, which facilitates subjecting the getter material to optimum temperatures for outgassin during the exhaust-of the tube and pro- Vides for maintaining the getter at desired operating temperatures during normal operation of thetube; m-

It is an object of my inventionato provide. a new and improved electric discharge-device; It is another ObjBOt'iOfmy inventiontoprovide a new and improvedigettering arrangementfig-for electric discharge devices of thetftype inwhich the getter operates throughout the life of the-tube to absorbgases from within the tube envelope.

In accordance with the illustrated embodiment of my invention, a'getter in the form of a :tubeor' sleeve of tantalumisconnectedin 'azcircuitfbetween a midtap to 'the'filamentary cathode and the cathode terminal-of thedischarge device. With this arrangement, a large current may be passed through the getter during exhaust of the tube by connecting the end terminals of the filament together and to one terminal of the supply of heatraised to the temperature range at whichthe compounds are readily-broken down and driven off during the exhaust, thereby .conditioning the getter I for efiective absorption of gases during 01):- erationrof the tube. With the illustrated embodig ment the heater orcathode current doesnot flow through the ggetter. during, operation oi'the tube. The getter isheated by radiation and conduction from the cathode and by the flow of; discharge current of the device through the tantalum sleeve. For a' better understanding of invention, reference may. be had-to the following description taken in connection with'the accompanying draw ing, and its scope will be pointed out in the-appended claims. In the 1 drawing, the single'figure is an elevational view, partially in section,- of an electric discharge device embodying my invention ..A- Referring now to the drawing, I have illustrated my invention as applied to a high power transmitting electric discharge device whichincludes an externally cooled anode l of tubular. configuration which is closed at one end and whichhas a flare portion 2 at the other end which issealed to a cylindrical glass member 3. Member 3'is in turn sealedto a vitreous; part 4 of a stemjconstruction designated generallypbythe numeral 5. The anode I, the glass cylinder 3 and the vitreous part of the stem construction cooperate to providev a hermeticallysealed envelope-for the dis-- charge device. 7 The vitreous portion 4 of the stem construction terminates in a flat cap 6 to which arefsealed a plurality of terminal prongs 1, 8v and 9; .A cathode construction including a pair of helical cathode elements l0 and ll'issupported within the anode l and in concentric relation with respect thereto by relatively rigid lead-in conductors l2 and l3'which extend through the cap of the stemconstructionand are weldedor othering voltage, with the other terminal connected to the midpoint of the cathode through the getter material. In this way the tantalum may be wise secured to the terminal prongs. l and .9,. respectively; 'The cathode elements l0 andg llmay :be secured to the lead-in conductors'in' any desired-manner and,-as illustrated, the overlapping end portions thereof. are bound together by wire wrappings I5. After assembly, a permanent union between the elements l0 and l l and lead-in conductors-13- and 14 may be effected by arc welding them'togetherfat the points designated by the numeral l6; An externally accessible connection with thecenter of the cathodeis provided by the terminal prong 8 which is connected to a lead-in conductor 11. Conductor I1 is connected with the lower ends of the cathode elements [0 and I I thr ugh a tantalum sleeve [8 and a short length of'c'ylindrical conductor I!) to which theends of the cathode elements are secured. As illustrated in the drawing, the elements are bound to conductor I 9 by a wire 20 and welded thereto, as illustrated by the numeral 2|.

A control grid construction is interposed between the cathode elements lll and II and the anode I. As illustrated in the drawing, this grid construction includes a flanged cylindrical supporting member 22 carried by lead-in conductors 23 and 24. It will be understood that lead-in conductors 23 and 24 extend through the vitreous cap 6 and are secured to terminal prongs similar to prongs 1-9, inclusive. The prongs have been omitted from the drawing in the interest of simplification. The controlling portion of the grid structure includes a plurality of supporting wires 25 which extend parell to the axis of the cylindrical anode I which is secured at one end to the grid supporting cylinder 22 and at the other end to a metal cap 26 which supports the lower ends of the wires 25 in spaced relation about the cathode construction. The grid structure is completed by the grid wire 21 which is spirally wrapped around the supporting wires 25.

During the operation of an electric discharge device constructed in accordance with the illustrated embodiment of my invention the heating current for the cathode is supplied by a source of' voltage connected with the terminal prongs 1 and 9. I The external connection for the space current between the anode and cathode is provided by the terminal 8. The tantalum sleeve l8 conducts this space current during operation of the tube which contributes to the heating thereof. More important, however, is its location in proximity to the heating cathode so that it is maintained at a desired temperature by heat radiated and conducted to it from the cathode. As stated earlier in the specification, for a tantalum sleeve the temperature range for effective absorption of gas is from 800 C. to 1600 C. The present construction affords an easy way of raising the tantalum sleeve l8 to a high temperature during exhaust of the tube. For example, by connecting terminal prongs 1 and 9 together and to one terminal of a source of volttage and the other terminal of the source to terminal prong 8, it is possible to conduct twice the rated heater current through the tubular sleeve l8 with onlyrated current through each half of the cathode. In this way, it is possible to raise the tantalum sleeve to a high temperature, above 1600 C., and eiTectively break down the compounds formed when gas is absorbed by the tantalum. I have found that with proper conditioning of the tantalum in this way and with the construction of the illustrated embodiment of my invention that much more effective gettering action is realized during normal operation of the tube.

While I have shown a particular arrangement of my invention in which the getter forms a portion of the cathode lead and also a part of the supporting structure for the cathode, it will be understood that other arrangements may be employed in which the getter is connected between an electrode of the discharge device and an externally accessible contact or terminal. It will'also be appreciated that my invention is not limited to the preferred material, tantalum, and that materials having similar properties, such as zirconium and molybdenum may be employed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric discharge device comprising an said cathode.

' 2. An electric discharge device comprising an evacuated envelope, a cathode supported within said envelope including a filament providing a hollow structure, a pair of externally accessible terminals, means connecting said terminals with said filament to provide for the application of heating current, a conductor sealed through said envelope, and a getter comprising. a tantalum member within. said envelope interconnecting said conductor and a point on said filament.

3. An electric discharge device comprising 2. directly heated cathode of the filamentary type Wound to provide a substantially hollow cylindrical structure, means connected with the ends of said filament and sealed through said envelope to provide externally accessible connections for a source of heating current, a tantalum sleeve having one end connected to the midpoint of said filament, and a conductor sealed through said envelope and electrically joined with the other end of said sleeve. I

4. An electric discharge device comprising a directly heated cathode of the filamentary type wound to provide a hollow structure, means connected to the ends of said filament and sealed through said envelope to provide externally accessible connections for a source of heating current, an element formed of material which readily absorbs gases when raised to an elevated temperature having one end connected to the midpoint of said filament, and a conductor sealed through said envelope and electrically joined with the other end of said element.

5. An electric discharge device comprising an ev cu ted envelope, a pair of externally accessible terminals, a cathode in the envelope comprising filament sections connected in series between said terminals and adapted to be heated to operating temperature by passage of current therethrough during operation of the device, a conductor sealed through the envelope wall and a tantalum getter member .connected to conduct current between said conductor and the junction of said filament sections, said tantalum member being proportioned and arranged to be heated to gas-absorbing temperature when said filament sections are heated during operation of the device and during exhaustion of the device to be heated to a higher outgassing temperature by passage of current through said tantalum member in series with said filament sections in parallel.

' JOHN W. FULTON. 

